Editas Medicine is to lose its chief medical officer at the end of the year, as the search is on for a new clinical leader.

Afterhours last night the biotech said in a brief update that Gerald Cox, M.D., Ph.D., “will be stepping down from the company at the end of the year.” No reason was given, and it’s not clear whether Cox will be turning up elsewhere in 2019.

“On behalf of the entire Editas team, I sincerely thank Gerry for his many contributions in helping translate the science of CRISPR into medicines,” said Katrine Bosley, president and CEO of Editas.

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“Gerry has been instrumental in shaping our clinical strategy, establishing our clinical operations, and advancing our LCA10 program to the cusp of the clinic. We look forward to working with him on a smooth transition through the end of the year and wish him well in his next endeavor.”

Cox has been at the biotech for nearly two years, coming before that from a major 16-year stint at Sanofi Genzyme as its VP of clinical development in rare diseases.

He added: “I have greatly enjoyed the privilege of working alongside a tremendous and talented team here at Editas Medicine, and together we have advanced the LCA10 program and other important genome editing programs.

“With this progress and the company’s overall evolution, the end of 2018 felt like a natural transition point. I look forward to working closely with the team on the submission of our IND for our LCA10 program and to seeing Editas Medicine’s continued success long-term.”

Editas had slated 2017 as the start date for its first clinical trials, but this was delayed due to manufacturing issues, with it now seeking a 2018 start date.

The Cambridge, Massachusetts-based company is focused on treating a form of severe blindness caused by a rare genetic disorder by using its CRISPR technology. Currently, this has only been done in animals by the biotech.

In its second quarter update earlier this month, Bosley said: “Our lead candidate, EDIT-101 to treat the genetic disease LCA10, is poised to be the first in vivo CRISPR medicine in human trials with an anticipated IND filing in October.”

Most of the big CRISPR biotech players have gone public in recent years, including Editas, as well as Intellia and CRISPR therapeutics, but all from very early-stage data and promise. This has seen their shares jump and fall on every paper coming out about the technology.

A few of those over the past year have indicated some of the potentially serious safety risks that can come with using CRISPR, sending stocks into the red, though most of the biotechs believe they can engineer their way around such issues.

In an interview this month with Bloomberg, Jennifer Doudna, an inventor of the CRISPR tech, said we’re around five to ten years away from an approved CRISPR drug, and that getting there will be no easy task.

“Can we today edit the DNA in human cells? Yes. Can we do it accurately? Yes. That’s absolutely being done in many labs around the world now,” Doudna said at a gene-editing summit at the Cold Spring Harbor Laboratory in New York to Bloomberg. “But the challenge is how to think about moving that into a clinical setting.”

Editas’ shares were down nearly 2.5% after normal trading hours, with a market cap of $1.46 billion.